JPH11307467A - Manufacture of silicon carbide semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure high activity and restrain an ill effect of high temperature treatment, by performing high temperature treatment after impurity ions and positively charged hydrogen ions are implanted in the same region. SOLUTION: In distribution of electron cloud 4 contributing to coupling gathering between a silicon atom 1 at a crystal lattice point and carbon atoms 2, a hydrogen ion 3 is implanted in the vicinity of the silicon atom 1 and the carbon atom 2. At this time, implantation condition of hydrogen ions is dosage to obtain concentration of about 10<20> -10<21> cm<-3> , because implantation of amount corresponding to the concentration of silicon atoms 1 and carbon atoms 2 is necessary. Hydrogen ions 3 are implanted in a range where the distribution of hydrogen 3 overlaps the distribution of impurity ions or includes it. After that high, temperature heat treatment is performed. As a result probability of substitution of impurity atoms and silicon atoms and diffusion can be accelerated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device made of silicon carbide, and more particularly to a method of implanting impurity ions thereof.

[0002]

2. Description of the Related Art For the purpose of controlling high frequency and high power, a power semiconductor device (hereinafter referred to as a power device) using silicon (hereinafter referred to as Si) has been improved in performance by various means. . However, the power device may be used in the presence of high temperature or radiation, and under such conditions, the Si power device may not be used.

Further, in response to a demand for a device having a higher performance than a Si power device, application of a new material is being studied. Silicon carbide (hereinafter referred to as Si)
The width of the forbidden band (referred to as C) is 3.26 eV for 4H type, 6
Since the H-type has 3.02 eV), the controllability of the electrical conductivity at a high temperature is excellent, and the maximum operating temperature can be increased. Also Si
Since it has a breakdown voltage that is about one order of magnitude higher, the on-resistance can be reduced, and power loss in a steady state can be reduced. It can be applied to high breakdown voltage elements. Further, since SiC has an electron saturation drift speed about twice as high as that of Si, it is also suitable for high frequency high power control. If such advantages of SiC can be exploited, it is considered that the characteristics of power devices can be dramatically improved, and MOSFETs, pn diodes, and the like are currently being prototyped.

When a semiconductor device such as a MOSFET or a pn diode is manufactured using SiC, a sophisticated element technology is required as in the case of a semiconductor manufacturing process using single crystal silicon. That is, it is necessary to establish a process technology such as epitaxially growing a SiC thin film, doping a donor or an acceptor, or forming a metal film or an insulating film after mirror-finishing the surface of the SiC substrate.

One of the most important process techniques is a technique for selectively forming impurity regions by introducing impurities. The method includes a thermal diffusion method and an ion implantation method. The thermal diffusion method widely used for Si semiconductor elements is difficult to apply in SiC because the diffusion coefficient of impurities is very small. Therefore, ion implantation is mainly used in SiC. In order to selectively form an impurity region, a photoresist or a thick oxide film of about 1 μm (formed using a low pressure CVD method or a thermal oxidation method) is partially formed on the surface of the SiC substrate, and the impurity is formed using this film as a mask. A method of irradiating ions may be used.

In Si, by heat treatment at 1000 ° C. for 30 minutes to 1 hour, impurity ions are diffused in Si, substitution occurs between silicon and implanted atoms, and impurity atoms are formed in the Si crystal. Activated as donor or acceptor. However, in SiC, heat treatment (hereinafter, referred to as annealing) is performed at a high temperature of about 1500 ° C. to activate the implanted impurity atoms. Boron (B) and aluminum (Al) are used as main acceptor atoms, and nitrogen (N) and phosphorus (P) are used as donor atoms. In SiC ion implantation,
In order to improve the activation rate of the implanted impurities, 800
It is also reported that ion implantation at a high temperature of １０００1000 ° C. is effective in improving the activation rate.

FIG. 5 is an explanatory view showing a conventional ion implantation and annealing temperature process. The vertical axis of the figure shows the SiC substrate temperature, and the horizontal axis shows the time required for processing. The impurity ions are implanted into the SiC substrate heated to a high temperature (up to 1000 ° C.) as described above. Here, since the time required for ion implantation is, for example, several tens of minutes for a wafer having a diameter of about 50 mm, the time for maintaining the peak temperature is also about several tens of minutes. After cooling to room temperature, a heat treatment is performed at about 1500 ° C., which is higher than that at the time of ion implantation, for about 30 minutes to 1 hour in an argon atmosphere or vacuum. As a furnace dedicated to heat treatment, for example, a furnace using tungsten as a heater and capable of raising the temperature to 2000 ° C. is used.

For example, boron ions B ⁺ are used as impurity ions, an acceleration voltage is 100 keV, and a dose is 3 × 10
¹⁵ cm ^-2 , 60 keV, 1.5 × 10 ¹⁵ cm ^-2 , 30 k
When continuous injection is performed under three conditions of eV and 1 × 10 ¹⁵ cm ⁻² ,
The distribution of impurity ions has a flat peak concentration (2 × 10 ²¹ cm ⁻³ ) up to about 0.4 μm from the surface, and the concentration drops sharply in a region deeper than that, and 0.5 μm from the crystal surface.
At a depth of m, the concentration is 1 × 10 ¹⁷ cm ⁻³ .

[0009]

As described above, the single crystal S
In iC, the implanted impurity atoms hardly diffuse even at a high temperature of around 1500 ° C., and the activation rate is low. The reason for the low diffusion coefficient and low activation rate is that
The interatomic distance of SiC is shorter than the closest interatomic distance of silicon.
This is considered to be due to the fact that the bond is hard to be broken.

In order to improve the activation rate of the ion-implanted impurities, it is considered necessary to perform high-temperature ion implantation by heating the substrate and high-temperature (1500 ° C.) and long-time heat treatment after the ion implantation. I have. However, as a result of the long-term heat treatment, silicon atoms evaporate from the crystal surface, so that the ratio of the surface to carbon atoms increases, and a phenomenon that the surface appears dark (blackening) has been reported. Further annealing at 1500 ° C. or more results in SiC
It has also been reported that irregularities running in the [1120] direction are generated on the crystal surface and become larger as the annealing temperature is increased. For example, while annealing at 1500 ° C. in vacuum has a surface roughness of about 95 nm in average amplitude, annealing at 1600 ° C. results in about 200 nm.

[0011] It is considered that the irregularities are generated due to the fact that in a high temperature region, the vapor pressure of Si increases and surface desorption occurs. Even in argon, it becomes about 55 nm at 1500 ° C., though not as much as in vacuum. As a result, there arises a problem that the mobility near the surface is reduced or the contact resistance is increased. In particular, MOSFET
Carrier transport in the layer induced near the surface is important, and mobility near the surface is greatly affected by the surface state.

In view of the above problems, it is an object of the present invention to provide a method of manufacturing a silicon carbide semiconductor device which can secure a high activation rate by a lower temperature heat treatment and can suppress the adverse effects of a high temperature treatment. is there.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of manufacturing a silicon carbide semiconductor device in which impurity ions are implanted into the surface of a semiconductor substrate made of silicon carbide single crystal or polycrystal and into the crystal. In the method, impurity ions and positively charged hydrogen ions are implanted into the same region, and then high-temperature heat treatment is performed.

By doing so, an effect of promoting the activation of the implanted impurities is obtained as described later. The mechanism is that the distribution of the electron cloud contributing to the bonds gathered between the silicon and carbon atoms of the silicon carbide crystal is distorted by the presence of implanted hydrogen ions, and the impurity atoms and silicon atoms or carbon atoms are distorted. It is believed that it promotes the probability of atomic substitution and diffusion.

The repetition of the implantation of positively charged hydrogen ions and the implantation of impurity ions and the simultaneous implantation of positively charged hydrogen ions and implantation of impurity ions maintain the hydrogen ion concentration at a high level. Is effective on
As a result, the activation of the implanted impurities is further promoted.

[0016]

[Embodiment 1] FIG. 1 is an explanatory view showing an ion implantation process according to the present invention, in which the vertical axis indicates the SiC substrate temperature and the horizontal axis indicates the time required for the processing. ing. Approximately 1 with the main surface slightly inclined from the (0001) plane
4H-Si grown with a 0 μm n-type epitaxial layer
A C wafer was prepared. At 1000 ° C, H ⁺ is accelerated to 40
keV, 1 × 10 ¹⁶ cm ⁻² , 30 keV, 1 × 10 ¹⁶ c
m ⁻² , 20 keV, 1 × 10 ¹⁶ cm ⁻² , 10 keV, 1
Continuous injection is performed under four conditions of × 10 ¹⁶ cm ^-2 . Then, 3 × 10 ¹⁵ c ions of aluminum (Al) were applied at 180 keV.
m ⁻² , 100 keV, 1.5 × 10 ¹⁵ cm ⁻² , 50 k
Continuous injection was performed at 1 × 10 ¹⁵ cm ⁻² at eV. next,
The wafer was annealed at 1400 ° C. for 30 minutes in a vacuum.

The distribution of impurity ions measured by XPS (X-ray photoelectron analysis) has a substantially flat peak concentration (2 × 10 ²¹ cm ⁻³ ) from the surface to about 0.4 μm. 0.5μ from surface
At a depth of m, the concentration was 1 × 10 ¹⁷ cm ⁻³ . The sheet resistance of this sample was evaluated by the van der Pauw method. The formation of the ohmic electrode was performed as follows. That is, nickel (Ni) electrodes are formed at four corners on the epitaxial layer of the sample by a sputtering method using a metal mask. The diameter of the electrode is 200 μm and the thickness is 400
nm. Thereafter, annealing was performed at 1050 ° C. for 5 minutes in an argon (Ar) atmosphere to obtain ohmic contact without rectification.

As a result, it was found that the sheet resistance was 5000 Ω / □, which is equivalent to that of the conventional 1500 ° C. annealing, even though the annealing temperature is 100 ° C. lower. The blackening of the surface was considerably suppressed as compared with the conventional case. That is, the activation rate could be increased by annealing at a lower temperature than in the past. The difference from the conventional method of FIG. 5 resides in that positively charged hydrogen ions are irradiated before the impurity ions are implanted. By filling the crystal with positively charged hydrogen ions, the following effects are considered to occur. FIG. 2 is a conceptual diagram of an atomic bonding state for explanation. 1 is a silicon atom, 2 is a carbon atom, and 3 is an implanted positively charged hydrogen ion.

The electron cloud 4 contributing to the bond gathered between the silicon atom 1 and the carbon atom 2 at the crystal lattice point
Is distorted by the presence of hydrogen ions 3 implanted near silicon atoms 1 and carbon atoms 2. Due to the distorted electron cloud 5, the electron density decreases between carbon atom 2 and silicon atom 1. As described above, the distribution of the electron cloud 4 involved in the bond between the silicon atom 1 and the carbon atom 2 becomes a distorted electron cloud 5, whereby the bond between the silicon atom 1 and the carbon atom 2 is weakened in the vicinity thereof, Since the probability that the bond is broken at a lower temperature is increased, the probability that the impurity atom is replaced with the silicon atom 1 or the carbon atom 2 is increased, and there is an effect of promoting diffusion.

In this case, the hydrogen ions 3 are implanted in an amount of about 10 ²⁰ to about 10 ²⁰ , because the implantation is required to have an amount corresponding to the concentration of the silicon atoms 1 and the carbon atoms 2 constituting the crystal.
^The injection amount is set to a concentration of about ²¹ cm ^-3 . Also,
It is necessary to perform the implantation in a range where the distribution of the hydrogen ions 3 overlaps with the distribution of the impurity ions or includes the distribution of the impurity ions.

[Embodiment 2] FIG. 3 is an explanatory view showing an ion implantation process according to the present invention.
The horizontal axis indicates the time required for processing, and the horizontal axis indicates the C substrate temperature.
The feature of this method is that implantation of impurity ions and implantation of hydrogen ions are repeated. The total implantation amount of impurity ions and hydrogen ions is the same as in the first embodiment.

In particular, in ion implantation at a high temperature, hydrogen ions diffuse out of the substrate from the time when the implantation is stopped (referred to as out diffusion). For this reason, the hydrogen ion concentration in the crystal rapidly decreases. With the decrease of hydrogen ion concentration in the crystal due to out diffusion,
The effect of promoting activation and diffusion by hydrogen ion implantation is lost.

As a countermeasure against this problem, in order to implant impurity ions in a state where the concentration of hydrogen ions in the crystal is high, it is preferable to repeat implantation of hydrogen ions and implantation of impurity ions. Although the actual implantation time of the impurity ions is about several minutes, the implantation time is divided into three times, and hydrogen ions are implanted before and after that. As a result, the activation temperature is further lowered by about 50 ° C. as compared with the above example. As a result, blackening and roughening of the silicon carbide substrate could be suppressed.

This is presumably because the impurity ions were implanted in a state where the hydrogen ion concentration was high. That is, the smaller the amount of implanted impurity ions, the less damage to the crystal due to ion implantation,
It is known that crystallinity is easily recovered by heat treatment. Therefore, in this embodiment, the same amount of impurity ions may be implanted several times to reduce the amount of implanted ions at a time, which would have been effective in recovering the crystal.

[Embodiment 3] In consideration of out diffusion of hydrogen ions, the best method for implanting impurity ions with a high hydrogen ion concentration is as follows.
This is a method of simultaneously implanting hydrogen ions and impurity ions. FIG. 4 is an explanatory view showing the ion implantation process according to the present invention, in which the vertical axis represents the temperature of the SiC substrate, and the horizontal axis represents the time required for processing.

An ordinary ion implanter can select only one type of ion to be implanted. Therefore, two injection systems
An ion implantation system with a system was prototyped and simultaneous implantation was attempted. The total implantation amount of impurity ions and hydrogen ions was the same as in the first embodiment. In this example, the activation temperature could be lowered by 200 ° C. as compared with the conventional case, and accordingly, the blackening and roughening of the silicon carbide substrate could be suppressed.

This is presumably because impurity ions were implanted with a high hydrogen ion concentration.

[0028]

As described above, according to the present invention, a method for manufacturing a silicon carbide semiconductor device in which impurity ions are implanted into a surface layer of a semiconductor substrate made of silicon carbide single crystal or polycrystal is provided. Charged hydrogen ions and impurity ions are implanted into the same region. The presence of the implanted hydrogen ions promotes the probability and diffusion of substitution of impurity atoms and silicon atoms or carbon atoms in the subsequent high-temperature heat treatment, so that the heat treatment temperature for activation can be lowered, and the high-temperature heat treatment Blackening and roughening of the surface can be suppressed.

Repeating the implantation of the positively charged hydrogen ions and the implantation of the impurity ions, and simultaneously performing the implantation of the positively charged hydrogen ions and the implantation of the impurity ions, activate the implanted impurities. Will further promote. These greatly contribute to the spread of silicon carbide semiconductor devices.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a temperature process according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the principle of operation of the present invention.

FIG. 3 is an explanatory view of a temperature process according to a second embodiment of the present invention.

FIG. 4 is an explanatory view of a temperature process according to a third embodiment of the present invention.

FIG. 5 is an explanatory view of a conventional temperature process.

[Explanation of symbols]

 Reference Signs List 1 silicon atom 2 carbon atom 3 hydrogen ion 4 electron cloud 5 distorted electron cloud

Claims (3)

[Claims] In a method of manufacturing a silicon carbide semiconductor device, wherein impurity ions are implanted into a surface layer of a semiconductor substrate made of silicon carbide single crystal or polycrystal, positively charged hydrogen ions and impurity ions are formed in the same region. And then performing a high-temperature heat treatment after the implantation. 2. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein the implantation of positively charged hydrogen ions and the implantation of impurity ions are repeated. 3. The method of manufacturing a silicon carbide semiconductor device according to claim 1, wherein the implantation of positively charged hydrogen ions and the implantation of impurity ions are simultaneously performed.